In a magnetic recording/reproducing device market, a demand has been made to improve a recording density at an annual rate of about 60%. Likewise, in a magnetic recording/reproducing head equipped in the magnetic recording/reproducing device, high performance has been demanded for both the characteristics of recording and reproduction.
It is important for a magnetic reproducing head to satisfy three technical challenges (1) to (3) stated below. (1) An improvement in a high sensitization technology, (2) an improvement in a narrowing technology of a track width, and (3) an improvement in a narrowing technology of a reproduction gap interval. In (1), when the recording density is 1 to 10 (Gb/in2) or less, the high recording density has been addressed choicely with an anisotropic magneto-resistive effect (AMR). When the recording density is higher, that is, 10 to 30 (Gb/in2), the high recording density has been addressed choicely with a giant magneto-resistive effect (GMR) by which a higher sensitivity can be obtained. Further, when the recording density is 20 to 70 (Gb/in2), the high recording density has been addressed choicely with an advance GMR effect called “a specular GMR” or “NOL-GMR”. In the advance GMR, an insulating oxide layer that is high in the reflectivity of electrons (specular reflection) or the like is interposed between interfaces of a GMR structure, and a multiple reflection effect of electron spin is intended for an increase in the output.
JP-A H4-358310 discloses a structure that is called “spin valve” in a magnetic head using GMR. The magnetic head includes a magneto-resistive effect element that is made up of a fixed layer which is made of a magnetic material and whose magnetization is fixed to a specific direction by means of an antiferromagnetic layer. The magneto-resistive element is further made up of a non-magnetic thin film that is laminated on the fixed layer, and a free layer formed of a magnetic film which is laminated through the non-magnetic thin film. The magneto-resistive effect element permits a relative angle between the respective magnetizations of the fixed layer and the free layer to change an electric resistance.
In addition, JP-A 2000-137906, JP-A 2001-168414 and JP-A 2001-230471 disclose an MR improved structure of a CIP-GMR. In the MR improved structure, an oxide layer is inserted into at least one of the free layer side and the fixed layer side, the multiple reflection of electrons is developed by means of the specular reflection of the oxide layer. With this structure, a rate of change in the resistance is improved. Also, JP-A 2002-190630 discloses a CIP-GMR structure in which a half-metal layer is interposed between the free layer and an intermediate layer or between the intermediate layer and the fixed layer.
At present, the development of higher sensitization requires a higher sensitive reproducing system. In 70 to 150 (Gb/in2), a tunnel magneto-resistive effect (TMR) that is very high in MR ratio is favorable from the viewpoint of an improvement in the sensitivity. In case of an ultra-high recording density that exceeds 150 (Gb/in2), it is conceivable that GMR (CPP-GMR) of a system that allows a detection current to flow in a direction perpendicular to a film surface may be brought to the mainstream while making the use of such an advantage that an element impedance is small. TMR is disclosed as a basic technology in JP-A H3-154217 as well as JP-A H10-91925.
CIP-GMR suffers from a problem related to insulation between an element and shields when a distance between the shields is shortened in order to address the high recording density. On the contrary, CPP-GMR does not deal with the insulation characteristics as a serious problem, and it is presumable that CPP-GMR is hardly affected by a thermal element breakdown that is attributable to an electrostatic voltage and current or nonlinearization that is attributable to a magnetic field. CPP-GMR has been numerously reported, and typical CPP-GMR is disclosed in JP-A H11-509956 and JP-A H7-221363.